1. Field of the Invention
The present invention relates to a decoupler and more particularly to an alternator decoupler for a serpentine accessory drive systems for automotive vehicles.
2. Description of Related Art
Serpentine accessory drive systems typically includes a driving pulley on the output shaft of the internal combustion engine of the vehicle, a series of driven pulleys for the accessories and a poly-V belt trained about the driving and driven pulleys. An advantage of the serpentine drive is that, by providing an automatic belt tensioner on the belt, the accessories can be fixedly mounted.
Particularly where the engine is of the four-cylinder type, the driving pulley establishes a highly dynamic loading on the belt. This high dynamic loading is due to the variable torque output characteristics of such engines. Under this circumstance, the tensioner cannot accommodate all of the variable torque characteristics. The result is sometimes noise and decreased belt life due to instantaneous belt slippage. It has been proposed to provide an engine crank shaft decoupler in order to deal with the high dynamic belt loading. This solution, while effective, is costly since the decoupler must have a capacity generally equal to the system capacity.
It has also been proposed in U.S. Pat. No. 5,139,463 of common ownership with the present invention and which is hereby incorporated by reference in its entirety for its teachings as they relate to the present invention, to provide an alternator assembly wherein a coil spring is provided between an alternator pulley and alternator hub structure for transmitting the driven rotational movements of the alternator pulley by the serpentine belt to the hub structure such that the alternator armature assembly is rotated in the same direction as the alternator pulley while being capable of instantaneous relative resilient rotational movements in opposite directions with respect to the alternator pulley during the driven rotational movement thereof. This has proven to be a cost effective manner of accommodating high dynamic belt loading to reduce noise and preserve belt life. Nevertheless, it can be appreciated that the coil spring employed is subject to significant stresses over the life of the alternator. It is therefore an object of the present invention to reduce stress on the spring and thereby increase the life thereof.